Bea Wain, who started singing on the radio at age 6, became a hit-making pop vocalist in the late 1930s and performed into her ninth decade as one of the last surviving singers of prominence from the big-band era, died Aug. 19 at an assisted-living community in Beverly Hills, Calif. She was 100.

The cause was congestive heart failure, said her daughter, Bonnie Barnes.

Largely self-taught, Ms. Wain had an expressive but understated swing style that propelled her career. She performed in nightclubs and on radio programs before her breakthrough in 1937 when arranger Larry Clinton selected her as the thrush for a band he was starting.

Clinton’s orchestra never achieved the enduring recognition of groups led by Glenn Miller, Tommy Dorsey, Artie Shaw or Benny Goodman. But with superb arrangements, a tightknit group of players and Ms. Wain out front, the ensemble had a solid commercial run with jukebox favorites such as “Deep Purple” and “Heart and Soul.”

The band made its biggest impression adapting classical compositions into popular swing numbers: notably “My Reverie,” from the Claude Debussy piano piece “Rêverie,” and “Martha,” from the Friedrich von Flotow opera of the same name.

In a 2007 radio interview , Ms. Wain said the Debussy estate in France initially balked when Clinton put words to the composer’s melody. His representatives were appalled by the idea, and no amount of money seemed to change their mind, she said.

The band recorded the number anyway, shipped a copy to France and then heard back: “If this girl sings it, Okay”

Ms. Wain’s negligible pay — $30 per recording session — began to grate on her. In early 1939, at the peak of her fame, she left Clinton and became a headliner on the college and theater circuit. She also was a regular on the popular radio program “Your Hit Parade,” where she became a friend of another guest, Frank Sinatra.

She was born Beatrice Wain on April 30, 1917, in New York, according to her daughter, although some sources say she had the last name Weinsier. Her father was a tailor, and she said her mother encouraged her early work on radio programs including the “NBC Children’s Hour,” where she earned $2 per broadcast.

She was in demand as a singer on radio shows hosted by Kate Smith, Fred Waring and Kay Thompson. Ms. Wain also cut records — initially under the name Beatrice Wayne — until record executives, without seeking her permission, tweaked her name to economize on space in credits.

Ms. Wain, who had married actor and radio announcer André Baruch, co-hosted a disc jockey series called “Mr. and Mrs. Music” on a New York station in the late 1940s and early 1950s. Later, they anchored a radio talk show in Palm Beach, Fla., before settling in Beverly Hills.

Baruch died in 1991. Survivors include two children, Bonnie Barnes of Glen Ellen, Calif., and Wayne Baruch of Los Angeles; and two grandchildren.

Her son helped produce the Three Tenors concerts featuring opera luminaries Luciano Pavarotti, Plácido Domingo and José Carreras. Ms. Wain said she attended a master class with Pavarotti during the tour and afterward found herself with the maestro.

“Somebody came over to him and said that I was a wonderful singer,” she told Christopher Popa, a Chicago music librarian who runs the website bigbandlibrary.com . “So he said, ‘Oh, I’d love to hear you.’ I said, ‘Well, as a matter of fact, I recorded one of the songs that you sing, that was ‘Martha’ . . . I said I did a swing version of it. And he said, ‘Show me, show me.’

“And I started to sing it. And he joined in — it was adorable — and he pretended he was a trombone player, and I’d sing la-la-la-la” to his trombone sounds. “And we had a lovely time.”